The present invention relates to a molding and/or vulcanizing press provided with a double-mold for molding or injecting materials, in particular elastomeric or plastomeric materials.
For preventing bad reciprocal coupling of the mold parts, which result from the deformation of the frame during the working cycles of the press, the present invention forsees coupling the mold parts with the supporting frame by means of pairs of matched surfaces, concave on the frames and convex on the molds, in particular cylindrical or spherical, such as to allow for relative shiftings to take place between the shut and pressurized molds and the frame.
The present invention concerns devices for molding as well as for injecting, and also for vulcanizing elastomeric or plastomeric articles. In particular, it refers to the vulcanizing presses that are provided with double-molds.
One type of such press that is by now well-known, is the one used in rubber technology and in particular, in tire technology, which is being widely used since it offers certain unquestioned advantages as with respect to those presses provided with a single-mold. In fact, with respect to these latter, the two-mold press has a double productivity, while the overall dimensions of the machine, its weight and its function are not equal twice that of the single-mold presses, so much so that further economic advantages are realized as far as regards the cost, and the consequent blocking of capital. Further savings can also be realized during operation, with regard to the usage of fluids and of energy in general, that are necessary for making the press function.
With respect to the single-mold presses, the double-mold presses however present a disadvantage that has a negative effect on the quality of the finished product which disadvantage has now become intollerable as a consequence of the high qualitative level obtained through the other systems and which seriously affect the actual possibilities of further developing machines.
The general architecture of a double-mold press consists of a frame comprising a base on which the two molds are arranged, a beam to which are connected the upper portions of the two molds and two shoulders that connect the extremities of the beam to the base by means of a kinematic connection (generally of the connecting rod-handle type) that allows for shifting the beam with respect to the base for opening and shutting the molds, for inserting the article to be molded and/or vulcanized and for removing the already molded or vulcanized article. Moreoever, this connection allows for keeping these molds shut during the molding and/or vulcanizing cycle.
As is already known, during the molding and vulcanizing of hollow articles such as, in particular, tires or injected articles, on the inside of the mold there acts a vulcanizingfluid pressure that is specifically introduced into the molds, or more precisely, in the article to be vulcanized, or the injection pressure of the material from which the article to be molded is comprised. This pressure tends to open the molds and hence, it must be resisted even before the entry of the fluid or the injected material into the mold, with a thrust exercised by the beam upon one portion of the mold against the other portion of the mold. If the beam is fixed at its extremities to the shoulders, and the thrust is applied onthe extremities for shutting the molds, while the molds exercise a pressure in the opposite sense at two intermediate points of the beam, then it can immediately be predicted that the beam bends more or less symmetrically with respect to its mid-plane between the two points of application for the counter-pressure of the molds. Owing to this flexing of the beam and hence of the consequent variation in the geometry of the machine, the two molds which have one portion made integral with the beam and the other portion made integral with the base of the press, present the two corresponding portions off-set one with respect to the other and hence, they result in being non-symmetrically loaded with regard to their axis and at times, they do not even keep completely shut, but each one tends to open-up in the zone overlooking the other mold. This phenomenon causes an unsymmetrical molding of the product and the formation of burrs that are more or less evident along a limited portion of the peripheral contour of the product and which compromise both its aspect as well as its qualitative standard.
It is evident that, in the single mold presses, the eventual bending of the beam however, is always centered in respect to the axis of the mold, which is why the machines are devoid of the above-described drawback.
The purpose of the present invention is to bring about certain improvements in the architecture of the double-mold presses so as to eliminate the above-mentioned defects and improve these machines and, in this manner, make available the undoubted advantages, previously discussed that they present.